Microstrip line is one of the most popular types of planar transmission lines, primarily because it can be fabricated by photolithographic processes and is easily integrated with other passive and active microwave devices. Microstrip line is a kind of “high grade” printed circuit construction, consisting of a track of copper or other conductor on an insulating substrate. There is a “backplane” on the other side of the insulating substrate, formed from similar conductor. The track is considered the “hot” conductor and the backplane is considered the “return” conductor. Microstrip is therefore a variant of a two-wire transmission line.
Conventional microstrip couplers are typically formed on the surface of a single semiconductor substrate. As such, the couplers operate in a two-dimensional plane. The maximum usable frequency range for these couplers is a function of the material used to form the microstrips, the length of the microstrips, the width of the microstrips and the spacing between coupling microstrips. With the advent of high-speed networks the need exists to implement coupling devices that have an increased maximum usable frequency range. Typically, space consumption on the substrate is a limiting factor in terms of increasing the maximum usable frequency range of the microstrip couplers. In most instances it is not feasible to increase the width and/or length of the microstrips in order to maximize the usable frequency range. Therefore, a need exists to develop a microstrip coupling mechanism that will realize increased maximum usable frequency range while limiting the amount of area consumed on the substrate.
While microstrips prevail as a mode of microwave signal transmission, waveguides provide for a similar transmission path for optical signals. Advances in optical sciences have recently been widely recognized for their impact in the field of communications. These advances have precipitated innovation towards an all-optical network, which includes; sources, modulators, wavelength division multiplexers, amplifiers and functional optical devices. Such an all-optical network would provide increased bandwidth. However, barriers still exist that prevent the total realization of an all-optical network. One key problem for both telecommunications and data communications in an all-optical environment is in the area of integration, i.e. being able to integrate and connect a myriad of optical devices in a confined space. In this regard, the increasing sophistication of the network leads to greater complexity. More network elements—such as multiplexers, de-multiplexers, lasers, modulators, etc.—need to share the limited space available on a substrate or semiconductor chip. Thus, in order to implement a fully optical network, it becomes increasingly important to integrate multiple optical elements while limiting the consumption of space.
Integrated optics technology is already finding wide applications in telecommunications and computer technology, and one can confidently expect that in the near future concepts like waveguides and optical network will have firmly entered the household usage. The developments of this future technology are still being carried out and improvements in this area include the need to develop integrated components and devices that minimize space consumption on the chip/substrate and accomplish this task in a cost effective manufacturing environment.